Magnetic actuated switch apparatus including shunt

ABSTRACT

A magnetic actuated switch apparatus including a shunt circuit for temporarily bypassing the switch in the absence of the magnet is described. Such apparatus is especially adapted for burglar alarm systems which require arming without setting off the alarm while opening the door in the process of departing from the premises. The switch is solid state in nature utilyzing an SCR or TRIAC as the shunting element for a magentic reed, and also incorporates means for preventing turn-on of the SCR or TRIAC when the magnetic reed opens upon subsequent opening of the door to the premises.

waited States Patent 1 Feldman MAGNETIC ACTUATED SWITCH APPARATUSINCLUDING SHUNT Irving B. Feldm'an, 1255 E. 101st St., Brooklyn, NY.11236 Filed: July 14, 1972 Appl. No.: 271,863

Inventor:

U.S. Cl. 317/1485 B, 340/274, 340/276 int. Cl. G08b 13/08 Field 01Search 317/DIG. 7; 307/93,

- References Cited UNITED STATES PATENTS 10/1970 Sellinger et al.11/1966 Teitelbaum.

1/1971 Casson 307/136 [111 7 3,769,556 Oct. 30, 1973 Primary Examiner-L.T. l-lix Attorney-Jack Oisher [5 7 ABSTRACT A magnetic actuated switchapparatus including a shunt circuit for temporarily bypassing the switchin the absence of the magnet is described. Such apparams is especiallyadapted for burglar alarm systems which require arming without settingoff the alarm while opening the door in the process of departing fromthe premises. The switch is solid state in nature utilyzing an SCR orTRIAC as the shunting element for a magentic reed, and also incorporatesmeans for preventing tum-on of the SCR or TRlAC when the magnetic reedopens upon subsequent opening of the door to the premises.

11 Claims, 3 Drawing Figures PANEL. I

BUZZER PAIENTED um 30 97a I BUZZER VOLTAGE FIG. 3

MAGNETIC ACTUATED SWITCH APPARATUS INCLUDING SHUNT This inventionrelates to magnetic actuated switch apparatus including a shuntingcircuit for temporarily preventing opening of the switch.

Commerical establishments having an exit door that opens outwardlyfrequently employ a burglar alarm system that when set by the lastperson to leave the premises becomes fully operative by the finalclosing of the exit door. The conventional system which has been in wideuse for many years employs a standard main panel containing a mainprotective relay with normally closed contacts, an alarmlocking relay,often a key actuated lock switch to turn the system on and off, andvarious terminals for connecting an alarm, a suitable DC power source,switches for the various openings to be protected, and a magnetic shunt,which is mounted adjacent the final exit door for cooperation with amagnet on the door. In operation,the last person to leave turns thesystem on, and then, while opening the exit door, depresses a button onthe magnetic switch. This permits him to leave and close the doorwithout sounding the alarm. However, the next time the door is openedthe alarm will sound.

One of the major problems in the use of such systems is the magneticactuated shunt.- Conventionally, it is a mechanical switch in which thebutton is mechanically held in its depressed position, maintaining apair of contacts closed, until magnetically actuated by the closingdoor. The frequent opening and closing of the contacts will ultimatelycause oxidation thereof and a build-up in resistance which in timerenders the switch inoperative. In addition, the various mechanicalparts of the switch do wear and the switch contacts can thusinadvertently open, causing a false alarm. As will be appreciated, falsealarms are highly irritating, inconvenient, and even costly.

The main object of the invention is a magnetic shunt.

switch for use with the standard panel as above described as a burglaralarm system for premises with an outwardly opening door wherein theabove-mentioned difficulties are substantially obviated. I

This and further objects of the invention as will appear hereinafter areachieved with a magnetic actuated switch comprising sealed contacts,such as of the magentic reed type, shunted by a solid state bistableelectronic switch, for example, an SCR or TRIAC, and with a push buttonswitch connected when depressed to turn-on the electronic switch. Afurther feature of the invention is the provision of means forpreventing turnon of the electronic switch when the magnetic reedcontacts open subsequent to the final closing of the door. In apreferred form, the last-named means comprises a capacitor connected inparallel across the electronic switch.

The construction of the invention is completely compatible with theexisting equipment employed in the installation of such known alarmsystems, especially in that the same standard panel can be used as inthe known systems. Thus, the magnetic shunt of the invention is an exactsubstitute for the known mechanical construction, but, with theexception of the button, having no moving parts eliminates completelythe difficulties above described with such known constructions.Moreover, since the contacts are sealed, build-up in resistance due tooxidation or dirt is substantially eliminated. Still further, the switchis smaller and of ligher 2 weight then the known type, which is alsoadvantageous.

Several exemplary forms of the invention will now be described ingreater detail with reference to the accompanying drawings, wherein:

FIG. 1 is a circuit diagram showing one embodiment of the magnetic shuntof the invention connected in a burglar alarm system;

FIG. 2 is a circuit diagram of another embodiment of the magnetic shuntof the invention;

FIG. 3 is a plan view of the actual magnetic shunt corresponding to theFIG. 1 embodiment.

FIG. 1 illustrates a typical burglar alarm system employing one form ofmagnetic shunt in accordance with the invention. It comprises a standardpanel 10, which can be purchased as a unit from various suppliers,comprising a main protective relay having a coil 11 and normally-closedcontacts 12, an alarm-locking relay having a coil 13 and normally opencontacts 14, and if desired a key-activated lock switch 15 with normallyopen contacts. The panel also comprises terminals l7, 18, 19, 20, 21,and 22. As shown, the protective relay coil 11 is connected to terminals21 an 22, the alarm locking relay coil 13 is connected to terminals 17and 18, the contacts 12 and 14 are connected in parallel between oneside of the lock switch 15 and terminal 19, the other side of lockswitch 15 is connected to terminal 17., and terminals 18 and 20 areinternally connected. The standard panel 10 is enclosed in dashed lines.The Serviceman need merely mount the panel near the exit door of thepremises, after which he installs a magnetic shunt switch generally onthe door jamb. A suitable magnet is then mounted on the door such thatwhen the door is in the closed position, the magnetic switch isactuated, whereas when the door is in an open position, the magneticswitch is deactivated. In FIG. I, the magnetic switch is designated 25and enclosed in dashed lines, and the activating magnet is schematicallyillustrated at 26.

The magnetic switch 25 comprises a normally-open magnetic reed switch28, a silicon controlled rectifier (SCR) 29 having anode A, cathode Cand gate G terminals, a capacitor 30 connected across the anode andcathode of the SCR, and a push-button switch 31 temporarily connectingwhen actuated the SCR gate to its anode; The cathode-anode circuit ofthe SCR is connected in parallel with the reed switch 28, one end ofwhich is connected to terminal 22 and the other end of which isconnected to terminal 19. The circuit is completed by connecting asuitable alarm, such as a buzzer or bell 32, to terminals 17 and 18, anda DC voltage source 33, such as a battery or rectified AC, across ter-'minals19 and 20. As is usual in such systems, the various openings tothe premises, such as other doors, windows, skylight, etc., are eachprotected by an electrical switch which is normally closed and which isconnected in series with the magnetic shunt 25 and the relay 11 viaterminal 22, all of these protective switches have been represented bythe single switch 8 in FIG. 1.

The operation is as follows. As will be observed, the buzzer 32 obtainspower from the battery 33 via the lock switch 15. Hence, so long as thelatter is off, the alarm can not be sounded. When the premises are to belocked up for the night, the last person to leave inserts a key into thelock switch 15 in order to turn on the alarm. If the final exit door isclosed, the magnet 26 is adjacent the reed switch 28, which closes,thereupon completing the circuit to the protective relay coil 11, whichopens the contacts 12, thereby maintaining the buzzer circuit open.Typically, the coil 11 has a resistance of about 300 ohms, and thebattery is 3-6 volts. It requires about 4 mA to activate the relay 311.If the door were now opened to permit the last person to exit from thepremises, the reed contacts 28 would open due to removal of the magnet26, which would open the protective relay coil 11 circuit, closing thecontacts 12 which would then complete the circuit to the alarm buzzer32. Simultaneously, the alarm holding relay I3 is activated closingcontacts 14. Thus the alarm continues to sound even if the door isclosed again and up until the lock switch 15 is actuated to turn off thesystem.

The magnetic shunt prevents sounding of the alarm when the door isopened as the last person leaves by shunting the reed switch 28. This isaccomplished by actuating the push button 31 as the door is opened. Thisaction temporarily puts anode potential on the gate turning on the SCRand maintaining the protective relay coil 11 circuit closed. Bistableelectronic switches, as a SCR or TRIAC, have the characteristic thatonce turned on it, remains on unit the anodecathode potential is reducedbelow its holding 'potential. This is accomplished when the front dooris closed by the closing of the reed switch 28 shorting out the SCRanode-cathode. Thus the SCR extinguishes, the last person has left thepremises without sounding the alarm, and the alarm is armed and ready tobe activated whenever the front door is reopened or any of the otheropenings to the premises forced thusopening switch 8. However, it hasbeen found that when the door is opened after arming of the alarm, thealarm does not sound as it is supposed to. In accordance with a featureof this invention, proper operation is achieved by means of thecapacitor connected across the reed switch 28. What apparently happenswithout the capacitor 30 is that, when the door opens opening the reedswitch 28 and thus'interrupting the relay coilll circuit, a voltage istemporarily induced across the relay coil 11. This voltage is inadditive relationship to the battery 33, with the result that theanode-cathode breakdown voltage of the SCR 29 is exceeded and the SCRturns on again shunting the reed switch and maintaining the relay llcircuit closed, thus preventing sounding of the alarm. What thecapacitor 30 apparently accomplishes is to short out the SCR for thistemporary induced voltage and thereby prevent unwanted triggering orturnon of the SCR. Thus, opening of reed switch 28 will sound the alarm.For this purpose, capacitor 30 should have a minimum amount ofcapacitance, to wit, at least 0.02 ufd. A value of 0.04 ufd hasprovensatisfactory.

In the embodiment illustrated in FIG. 1 employing an SCR or thyristor,it is essential that the magnetic switch 25 be connected to terminals 19and 22 such that the positive side of battery 33 is connected to the SCRanode, and the negative side to the SCR cathode. The

magnetic switch in accordance with the invention illustrated in FIG. 2eliminates the foregoing requirement. The parts ofthe circuit that arethe same as in FIG. I bear the same reference numerals. The soledifference is the substitution of a TRIAC 41 for the SCR. TRlACs havebi-directional characteristics, and can be operated and turned on by avoltage of either polarity. The TRIAC otherwise behaves similarly to anSCR. Thus, the polarity of the applied voltage, or the connections tothe battery, become unimportant. This simplifies wiring of the system.

FIG. 3 illustrates a suitable package for the magnetic switch 25illustrated in FIG. 1. It comprises an elongated rectangular casing orcan 42, for example of plastic, provided with lugs 43 for mounting sameon the door jamb. On the side of the casing are terminals 44 to whichare connected the various circuit components which are all housed withinthe casing, as shown. The

components may be potted in a suitable plastic. The

magnet to activate the reed would generally have a similarconfiguration. The push-button of the switch 31 protrudes through thetop casing wall and is thus readily accessible for manual activation.

In a typical circuit, the SCR is of the low current size of the order ofa few watts since it need not dissipate much power, it beingconventional to employ as the battery 33 a 3 volt source. Thus all ofthe switch components are easily fitted within a single casing 42 havingdimensions of approximately 2% inches long, with a cross-section ofabout /2 inches square. The resultant switch is thus of small size andweight. Moreover, it is quite inexpensive to manufacture, employing asit does only a few inexpensive components. Nevertheless, it providesperformance that far exceeds that of the conventional mechanicalmagnetic shunt. The switch of the invention has a much longer lifetime,due to the sealing of the reed contacts. Moreover, the absence ofmechanical parts substantially eliminates false alarms due to mechanicalwear and tear. Still further, the spacing of the actuating magnet to theshunt is less critical than in the known construction. Finally, theseimportant improvements are obtained with a magnetic shunt that iscompletely compatible with the existing panels thus avoiding the needfor rewiring of the latter.

While only the door actuated reed switch 28 and one other switch 8 areshown, it is understood, as is well known, that other door and windowswitches can be connected in series with the relay coil 11 such that theunauthorized opening of any of these will interrupt the relay circuitsounding the alarm. While my invention has been described in connectionwith specific embodiments thereof, those skilled in the art willrecognize that various modifications are possible within the principlesenunciated herein and thus the present invention is not to be limited tothe specific embodiments disclosed.

What is claimed is:

1. A magnetic actuated switch with incorporated shunt circuit for use inalarm systems, comprising nor .mally-open contacts which will close inresponse to a locally provided magnetic field, a bistable electronicswitch having main terminals and a turn-on connection, the mainterminals of the electronic switch being connected in parallelwith thenormally-open contacts, a

source of D.C. voltage, means for connecting the D.C.

- sourceto the normally-open contacts whereby closing field whichreopens the normally open contacts interrupting the load circuit andcreating a temporary condition tending to turn-on the electronic switch,and means operatively coupled to the electronic switch for preventingturn-on thereof when the normally-open contacts reopen to therebyprevent undesired reclosing of the interrupted load circuit.

2. A magnetic actuated switch as set forth in claim 1 wherein theturn-on preventing means for the electronic switch comprises a capacitorconnected in parallel with the switch main terminals.

3. A magnetic actuated switch asset forth in claim 2 wherein thecapacitor has a capacitance of at least 0.02 #fd.

4. A magnetic actuated switch as set forth in claim 2 wherein theelectronic switch comprises an SCR having anode and cathode mainterminals and a gate connection, the capacitor is connected across theanode and cathode, and a push button is provided for temporarilyconnecting the gate to the anode.

5. A magnetic actuated switch as claimed in claim 2 wherein theelectronic switch comprises a TRIAC having two anode main terminals anda gate connection, the capacitor is connected across the two anodes, anda push button is provided for temporarily connecting the gate to one ofthe anodes.

6. A magnetic actuated switch as set forth in claim 3 wherein thenormally-open contacts are part of a magbeing inside the housing withits main terminals connected to the housing terminals and with its gateconnected to one side of the push button, the other side of 6 the pushbutton being connected to one of the housing terminals.

8. A burglar alarm system comprising a magnetic actuated switch asclaimed in claim 1, in combination with a panel comprising a protectiverelay havng a coil and normally closed contacts which are maintainedopen upon energization of the coil, said protective relay coil beingconnected in series with the magnetic actuated switch normally opencontacts and constituting the said external load circuit, said D.C.source being connected in series with the said coil and the magneticactuated switch, an outwardly opening door, and a magnet mounted on thedoor and adapted to close the normally-open contacts when the door is ina closed position.

9. A burglar alarm system as claimed in claim 8 and further including analarm device connected in series with the contacts of the protectiverelay and causing an alarm when the latter close in reponse tointerruption of the load circuit.

10. A burglar alarm system as claimed in claim 9 and further includingon the panel a holding relay for the alarm device and adapted tomaintain the alarm device circuit closed when actuated to sound thealarm.

11. A burglar alarm system comprising a magnetic actuated switch asclaimed in claim 7, in combination with a separate panel comprising aprotective relay having a coil and normallyclosed contacts which aremaintained open upon energization of the coil, said protective relaycoil being connected in series with the magnetic actuated switch and theDC source and constituting the external load circuit, an outwardlyopening door, a magnet mounted on the door and adapted to close thenormally-open contacts when the door is in a closed position, an alarmdevice connected in series with the contacts of the protective relay,and a holding relay on the panel for the alarm device and adapted tomaintain the alarm device circuit closed when actuated to sound thealarm.

1. A magnetic actuated switch with incorporated shunt circuit for use inalarm systems, comprising normally-open contacts which will close inresponse to a locally provided magnetic field, a bistable electronicswitch having main terminals and a turn-on connection, the mainterminals of the electronic switch being connected in parallel with thenormally-open contacts, a source of D.C. voltage, means for connectingthe D.C. source to the normally-open contacts whereby closing of thecontacts enables application of D.C. voltage to an external loadcircuit, means for temporarily connecting the electronic switch turn-onconnection to the D.C. source for turning on the electronic switch toshunt the normally-open contacts allowing application of the D.C.voltage to the external load circuit, said electronic switch turning offwhen the normally-open contacts close in response to the magnetic fieldwhereby the D.C. voltage continues to be applied to the external loadcircuit, the next removal of the magnetic field which reopens thenormally open contacts interrupting the load circuit and creating atemporary condition tending to turn-on the electronic switch, and meansoperatively coupled to the electronic switch for preventing turn-onthereof when the normally-open contacts reopen to thereby preventundesired reclosing of the interrupted load circuit.
 2. A magneticactuated switch as set forth in claim 1 wherein the turn-on preventingmeans for the electronic switch comprises a capacitor connected inparallel with the switch main terminals.
 3. A magnetic actuated switchas set forth in claim 2 wherein the capacitor has a capacitance of atleast 0.02 Mu fd.
 4. A magnetic actuated switch as set forth in claim 2wherein the electronic switch comprises an SCR having anode and cathodemain terminals and a gate connection, the capacitor is connected acrossthe anode and caThode, and a push button is provided for temporarilyconnecting the gate to the anode.
 5. A magnetic actuated switch asclaimed in claim 2 wherein the electronic switch comprises a TRIAChaving two anode main terminals and a gate connection, the capacitor isconnected across the two anodes, and a push button is provided fortemporarily connecting the gate to one of the anodes.
 6. A magneticactuated switch as set forth in claim 3 wherein the normally-opencontacts are part of a magnetic reed switch.
 7. A magnetic actuatedswitch as claimed in claim 6 and further comprising a housing having twoterminals and a push-button, said reed switch being inside the housingwith its normally-open contacts connected to the housing terminals, saidcapacitor being inside the housing and being connected to the housingterminals, said electronic switch being an SCR or TRIAC having mainterminals and a gate turn-on connection and being inside the housingwith its main terminals connected to the housing terminals and with itsgate connected to one side of the push button, the other side of thepush button being connected to one of the housing terminals.
 8. Aburglar alarm system comprising a magnetic actuated switch as claimed inclaim 1, in combination with a panel comprising a protective relayhaving a coil and normally closed contacts which are maintained openupon energization of the coil, said protective relay coil beingconnected in series with the magnetic actuated switch normally opencontacts and constituting the said external load circuit, said D.C.source being connected in series with the said coil and the magneticactuated switch, an outwardly opening door, and a magnet mounted on thedoor and adapted to close the normally-open contacts when the door is ina closed position.
 9. A burglar alarm system as claimed in claim 8 andfurther including an alarm device connected in series with the contactsof the protective relay and causing an alarm when the latter close inreponse to interruption of the load circuit.
 10. A burglar alarm systemas claimed in claim 9 and further including on the panel a holding relayfor the alarm device and adapted to maintain the alarm device circuitclosed when actuated to sound the alarm.
 11. A burglar alarm systemcomprising a magnetic actuated switch as claimed in claim 7, incombination with a separate panel comprising a protective relay having acoil and normallyclosed contacts which are maintained open uponenergization of the coil, said protective relay coil being connected inseries with the magnetic actuated switch and the D.C. source andconstituting the external load circuit, an outwardly opening door, amagnet mounted on the door and adapted to close the normally-opencontacts when the door is in a closed position, an alarm deviceconnected in series with the contacts of the protective relay, and aholding relay on the panel for the alarm device and adapted to maintainthe alarm device circuit closed when actuated to sound the alarm.